1. Field of the Invention
This invention relates to methods and systems for the treatment of conduction disturbances of the heart. More particularly, this invention relates to validating and monitoring percutaneous cardiac ablation procedures.
2. Description of the Related Art
Atrial fibrillation is a well-known disorder of the heart, which causes hemodynamic efficiency to be reduced and which, in serious cases, can lead to cardiac embolization, stroke, ventricular arrhythmias and other potentially fatal complications. Atrial fibrillation is frequently engendered by abnormal electrical conduction paths within the heart muscle. Normally, electrical activation signals are conducted in an orderly way through the atrium and into the ventricle, passing each point in the heart only once in each heart cycle. Electrical activation signals at different locations in the heart are well correlated, taking into account normal propagation delays from one region of the heart to another. In response to local activation signals, the atrial muscle fibers contract in proper synchrony, to pump blood through the atrium. In atrial fibrillation, however, this orderly contraction is lost, it is believed, as multiple, changing, spatially disorganized activation wavelets sweep across the surface of the atria, resulting in irregular patterns of electrical activation. A given atrial muscle fiber is activated to contract multiple times in each heart cycle, and fibrillation takes the place of normal contraction. These phenomena are described in detail by Gregory W. Botteron and Joseph M. Smith in an article entitled, “A Technique for Measurement of the Extent of Spatial Organization of Atrial Activation During Atrial Fibrillation in the Intact Human Heart,” in IEEE Transactions on Biomedical Engineering, 12 (June 1995), pages 579-586, and in a second article entitled, “Quantitative Assessment of the Spatial Organization of Atrial Fibrillation in the Intact Human Heart,” in Circulation 93 (Feb. 1, 1996), pages 513-518. Both of these articles are incorporated herein by reference.
Invasive cardiac ablation techniques for the treatment of arrhythmias such as described above are well known in the art. For example, U.S. Pat. Nos. 5,443,489 and 5,480,422, issued to Ben-Haim describe systems for ablating cardiac tissue. U.S. Pat. No. 5,807,395, issued to Mulier et al., and U.S. Pat. No. 6,190,382, issued to Ormsby et al., describe systems for ablating body tissue using radiofrequency energy. U.S. Pat. Nos. 6,251,109 and 6,090,084, issued to Hassett et al., 6,117,101, issued to Diederich et al., 5,938,660 and 6,235,025, issued to Swartz et al., 6,245,064, issued to Lesh et al., 6,164,283, 6,305,378 and 5,971,983, issued to Lesh, 6,004,269, issued to Crowley et al., and 6,064,902, issued to Haissaguerre et al., describe apparatus for tissue ablation to treat atrial arrhythmia. U.S. Pat. No. 5,366,490, issued to Edwards et al., describes a method for applying destructive energy to a target tissue using a catheter.
Radiofrequency ablation using multiple contiguous circumferential points, guided by electro-anatomical mapping is proposed in the document, Circumferential Radiofrequency Ablation ofpulmonary Vein Ostia: A New Anatomic Approach for Curing Atrial Fibrillation, Pappone C, et al., Circulation 102:2619-2628 (2000).
U.S. Pat. No. 6,743,225, issued to Sanchez et al., proposes to measure electrical activity of the cardiac tissue proximate a lesion site during an ablation treatment, and then to compare the measurements in order to determine whether the lesion is clinically efficacious so as to be able to block myocardial propagation. For example, the standard deviation of the amplitude of the electrocardiogram signal has been used as a metric.
U.S. Pat. No. 5,954,665, issued to Ben-Haim, the disclosure of which is herein incorporated by reference, describes a cardiac catheter having two electrodes, spaced apart. In operation, there is a measurable propagation delay between activation signals at the two electrodes under conditions of normal conduction. The catheter is manipulated so as to position the ablation device in contact with the endocardium at the site of a suspected abnormal conduction path. First and second pre-ablation signals, responsive to the heart's activation signals, are received from the two electrodes, respectively, preferably simultaneously, or alternatively successively. A correlation coefficient of the first and second pre-ablation signals is computed. An ablation device is then activated so as to ablate the endocardium at the site, preferably by applying radiofrequency energy thereto. After the ablation is completed, and the ablation device is deactivated, first and second post-ablation signals are respectively received from the first and second electrodes, and the correlation coefficient is again computed. If the pre- and post-ablation correlation coefficients are substantially the same, the ablation is determined to have been insufficient to interrupt the abnormal conduction path. If the post-ablation correlation coefficient is substantially less than or greater than the pre-ablation coefficient, however, the ablation is considered to have been effective in interrupting the abnormal path.
It has also been proposed to produce circumferential ablative lesions using ultrasound delivered through a balloon. This technique is described, for example, in the document, First Human Experience With Pulmonary Vein Isolation Using a Through-the-Balloon Circumferential Ultrasound Ablation System for Recurrent Atrial Fibrillation, Natale A, et al., Circulation 102:1879-1882 (2000).